Integrated fluid coking paraffin dehydrogenation process

ABSTRACT

An integrated fluid coking/paraffin dehydrogenation process. The fluid coking unit is comprised of a fluid coker reactor, a heater, and a gasifier. Solids from the fluidized beds are recycled between the coking zone and the heater and between the heater and the gasifier. A separate stream of hot solids from the gasifier is passed to the scrubbing zone after first being reduced in temperature by introduction of an effective amount of diluent, such as steam. A light paraffin stream is introduced into this stream of hot solids between the point where the diluent is added and the scrubbing zone. The hot particles act to catalyze the dehydrogenation of paraffins to olefins.

FIELD OF THE INVENTION

The present invention relates to an integrated fluid coking/paraffindehydrogenation process. The fluid coking unit is comprised of a fluidcoker reactor, a heater, and a gasifier. Solids from the fluidized bedsare recycled between the coking reactor and the heater and between theheater and the gasifier. A separate stream of hot solids from thegasifier is passed to the scrubbing zone of the coking reactor afterfirst being reduced in temperature by introduction of an effectiveamount of diluent, such as steam. A light paraffin stream is introducedinto this stream of hot solids between the point where the diluent isadded and the scrubbing zone. The hot particles act to catalyze thedehydrogenation of paraffins to olefins.

BACKGROUND OF THE INVENTION

Transportation fuels, particularly motor gasoline, contain a relativelyhigh level of aromatic components, such as benzene. These fuels, whilerelatively high in octane number, are facing ever growing difficultly inmeeting environmental regulations with regard to emissions. This isprimarily because of their high level of aromatics. Consequently, muchwork is being done to develop what has become known as "low emissionsfuels". An important aspect of this work involves the substitution ofnon-aromatic components, having a relatively high octane value, foraromatic components of the fuel.

A class of non-aromatic components having relatively high octane value,which has been proposed for the production of low emissions fuels, isoxygenates. Non-limiting examples of preferred oxygenates for fuelsinclude the unsymmetrical dialkyl ethers, particularly methyl tert-butylether (MTBE), ethyl tert-butyl ether (ETBE), and tert-amylmethyl ether(TAME). Conventional methods for the manufacture of MTBE include thereaction of iso-butylene with methanol over cation-exchanged resins.This has created a significant demand for iso-butylene. Furthermore,there is also a demand in the chemical industry for other low carbonnumber olefins.

Low carbon number olefins, for example those having 2 to 10 carbonatoms, are typically obtained by the dehydrogenation of thecorresponding paraffinic hydrocarbon. One method for light paraffindehydrogenation is the so-called oxidative dehydrogenation processwherein light alkanes are reacted with oxygen over a mixed metal oxidecatalyst to produce a mixture of olefin, water, CO_(x), and unreactedparaffin. While high conversions combined with high olefin selectivitiescan be achieved, this process has a number of disadvantages. Onedisadvantage is the loss of fuel value because of water and CO_(x)formation. Another disadvantage concerns the relatively high costs ofrunning the process. There are also problems concerning hazardsassociated with exothermic combustion reactions.

A more direct and preferred approach for producing low carbon numberolefins is direct dehydrogenation over a suitable catalyst to produceolefins and molecular hydrogen. This chemistry has recently receivedconsiderable interest, although high reaction temperatures in the rangeof 500° C. to 650° C. are required to obtain a significant equilibriumyield (e.g., 15-65%) of olefin. Moreover, under these reactionconditions light alkane hydrogenolysis to methane and ethane is acompeting undesirable reaction. Most catalysts studied to date have notshown suitable selectivities for dehydrogenation versus hydrogenolysis.They have also suffered from rapid deactivation, necessitating frequentregeneration. As a consequence, the process economics have not beenclearly favorable. Large incentives exist for catalysts which showrelatively high selectivity for olefins and which have improvedresistance to deactivation. It is also desirable that the catalyst becapable of being regenerated using relatively inexpensive procedures,such as treatment with air.

It was found by the inventors hereof that a carbonaceous catalyst willeffectively catalyze the dehydrogenation of light alkanes. This is thesubject of U.S. patent application Ser. No. 07/900,977, filed Jun. 18,1992, which is incorporated herein by reference.

One source of carbonaceous material in some modern complex petroleumrefineries is in fluid coking process units. In conventional fluidcoking, in a process unit comprised of a coking reactor and a heater, orburner, a petroleum feedstock is injected into the reactor in a cokingzone comprised of a fluidized bed of hot, fine, coke particles and isdistributed uniformly over the surfaces of the coke particles where itis cracked to vapors and coke. The vapors pass through a cyclone whichremoves most of the entrained coke particles. The vapor is thendischarged into a scrubbing zone where the remaining coke particles areremoved and the products cooled to condense the heavy liquids. Theresulting slurry, which usually contains from about 1 to about 3 wt. %coke particles, is recycled to extinction to the coking zone.

The coke particles in the coking zone flow downwardly to a strippingzone at the base of the reactor vessel where steam removes interstitialproduct vapors from, or between, the coke particles, and some adsorbedliquids from the coke particles. The coke particles then flow down astand-pipe and into a riser which moves them to a burner, or heatingzone where sufficient air is injected for burning at least a portion ofthe coke and heating the remainder sufficiently to satisfy the heatrequirements of the coking zone where the unburned hot coke is recycled.Net coke, above that consumed in the burner, is withdrawn as productcoke.

Another type of fluid coking employs three vessels: a coking reactor, aheater, and a gasifier. Coke produced in the coking reactor is withdrawnand is passed to the heater where a portion of the volatile matter isremoved. The coke is then passed to the gasifier where it reacts, atelevated temperatures, with air and steam to form a mixture of carbonmonoxide, carbon dioxide, methane, hydrogen, nitrogen, water vapor, andhydrogen sulfide. The gas produced in the gasifier is passed to theheater to provide part of the heater heat requirements. The remainder ofthe heat is supplied by circulating coke between the gasifier and theheater. Coke is also recycled from the heater to the coking reactor tosupply the heat requirements of the reactor.

There is a need in the art for producing olefins in a more costefficient manner, especially if a cheap source of catalyst, such as cokefrom a fluid coking unit could be used.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided anintegrated process for converting a heavy hydrocarbonaceous chargestockto lower boiling products and for converting light paraffins to olefins.The process is performed in a fluid coking process unit comprised of afluid coking reactor, a heater, and a gasifier. A stream of hot solidsis recycled between the coking zone and the heater and between theheater and the gasifier. A separate stream of hot solids is passed fromthe gasifier to the scrubbing zone after first being reduced todehydrogenation temperature by use of introduction of a diluent. Olefinsare produced by introducing a stream of C₂ to C₁₀ paraffins into thestream of hot solids passing from the gasifier to the scrubbing zone, ata point between the introduction of the diluent and the point ofintroduction of solids from the heater. The fluid coking reactorcontains a coking zone, a scrubbing zone located above the coking zonefor collecting vapor phase products, and a stripping zone at the bottomof the coking reactor for stripping hydrocarbons from solid particlespassing downwardly through the coking zone where they exit and arepassed to the heating zone. Vapor phase products are separated in thescrubbing zone.

In a preferred embodiment of the present invention, the paraffin streamwhich is introduced into the solid particle stream passing from theheating zone to the coking zone are C₂ to C₆ paraffins.

In yet another preferred embodiment of the present invention, thediluent is selected from the group consisting of steam, methane,nitrogen, carbon dioxide, and hydrogen, hydrogen sulfide or mixturesthereof. Also, BTU fuel gas.

In another preferred embodiment of the present invention, the cokingzone is operated at a temperature from about 450° C. to 650° C. and apressure from about 0 to 150 psig.

In still another preferred embodiment of the present invention, thechargestock is selected from the group consisting of heavy and reducedpetroleum crudes, petroleum atmospheric distillation bottoms, petroleumvacuum distillation bottoms, pitch, asphalt, bitumen, and liquidproducts derived from a coal liquefaction process.

BRIEF DESCRIPTION OF THE FIGURE

The sole FIGURE herein is a schematic flow plan of a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Suitable heavy hydrocarbonaceous feedstocks for use in the presentinvention include heavy hydrocarbonaceous oils, heavy and reducedpetroleum crude oil; petroleum atmospheric distillation bottoms;petroleum vacuum distillation bottoms, or residuum; pitch; asphalt;bitumen; other heavy hydrocarbon residues; tar sand oil; shale oil;coal; coal slurries; liquid products derived from coal liquefactionprocesses, including coal liquefaction bottoms; and mixtures thereof.Such feeds will typically have a Conradson carbon content of at least 5wt. %, generally from about 5 to 50 wt. %. As to Conradson carbonresidue, see ASTM Test D189-165. Preferably, the feed is a petroleumvacuum residuum.

A typical petroleum chargestock suitable for the practice of the presentinvention will have the composition and properties within the ranges setforth below.

    ______________________________________                                        Conradson Carbon   5 to 40 wt. %                                              Sulfur             1.5 to 8 wt. %                                             Hydrogen           9 to 11 wt. %                                              Nitrogen           0.2 to 2 wt. %                                             Carbon             80 to 86 wt. %                                             Metals             1 to 2000 wppm                                             Boiling Point      340° C.+ to 650° C.+                         Specific Gravity   -10 to 35° API                                      ______________________________________                                    

Reference is now made to the FIGURE, which shows a fluid coking processunit containing a coker reactor 1, a heater 2 and a gasifier 3. A heavyhydrocarbonaceous chargestock is passed via line 10 to coking zone 12 ofcoker reactor 1, which coking zone contains a fluidized bed of solid, orso-called "seed" particles having an upper level indicated at 14.Although it is preferred that the solid particles be coke particles,they may be any other suitable refractory material. Non-limitingexamples of such other suitable refractory materials are those selectedfrom the group consisting of silica, alumina, zirconia, magnesia, ormullite, synthetically prepared or naturally occurring material such aspumice, clay, kieselguhr, diatomaceous earth, bauxite, and the like. Thesolids will have an average particle size of about 40 to 1000 microns,preferably from about 40 to 400 microns.

A fluidizing gas e.g. steam, is admitted at the base of coker reactor 1,through line 16, into stripping zone 13 of the coker reactor in anamount sufficient to obtain superficial fluidizing velocity. Such avelocity is typically in the range of about 0.5 to 5 ft/sec. A portionof the decomposed feed forms a fresh coke layer on the fluidized solidparticles. The solids are partially stripped of fresh coke and occludedhydrocarbons in stripping zone 13 by use of said steam and passed vialine 18 to heater 2. Coke at a temperature above the coking temperature,for example, at a temperature from about 40° C. to 200° C., preferablyfrom about 65° C. to 175° C., and more preferably about 65° C. to 120°C. in excess of the actual operating temperature of the coking zone isadmitted to reactor 1 by line 42 in an amount sufficient to maintain thecoking temperature in the range of about 450° to 650° C.

The pressure in the coking zone is maintained in the range of about 0 to150 psig, preferably in the range of about 5 to 45 psig. Conversionproducts are passed through cyclone 20 of the coking reactor to removeentrained solids which are returned to the coking zone through 22. Thevapors leave the cyclone through line 24, and pass into a scrubber 25 atthe top of the coking reactor. If desired, a stream of heavy materialscondensed in the scrubber may be recycled to the coking reactor via line26. The coker conversion products are removed from the scrubber 25 vialine 28 for fractionation in a conventional manner. The olefins whichare generated by contacting the paraffin stream with hot solids in line35 are removed via this line 28 and recovered downstream byfractionation.

In heater 2, stripped coke from coking reactor 1 (cold coke) isintroduced by line 18 to a fluid bed of hot coke having an upper levelindicated at 30. The bed is partially heated by passing a fuel gas intothe heater by line 32. Supplementary heat is supplied to the heater bycoke circulating from gasifier 3 through line 34. The gaseous effluentof the heater, including entrained solids, passes through a cyclonewhich may be a first cyclone 36 and a second cyclone 38 wherein theseparation of the larger entrained solids occur. The separated largersolids are returned to the heater bed via the respective cyclone diplegs39. The heated gaseous effluent which contains entrained solids isremoved from heater 2 via line 40.

As previously mentioned, hot coke is removed from the fluidized bed inheater 2 and recycled to coking reactor by line 42 to supply heatthereto. Another portion of coke is removed from heater 2 and passed vialine 44 to a gasification zone 46 in gasifier 3 in which is alsomaintained a bed of fluidized solids to a level indicated at 48. Ifdesired, a purged stream of coke may be removed from heater 2 by line50.

The gasification zone is maintained at a temperature ranging from about870° C. to 1100° C. at a pressure ranging from about 0 to 150 psig,preferably at a pressure ranging from about 25 to about 45 psig. Steamvia line 52, and an oxygen-containing gas, such as air, commercialoxygen, or air enriched with oxygen via line 54, and passed via line 56into gasifier 3. The reaction of the coke particles in the gasificationzone with the steam and the oxygen-containing gas produces a hydrogenand carbon monoxide-containing fuel gas. The gasified product gas, whichmay contain some entrained solids, is removed overhead from gasifier 3by line 32 and introduced into heater 2 to provide a portion of therequired heat as previously described.

In accordance with the present invention, olefins are produced bydehydrogenation of paraffins in line 35 which contains hot solids whichare being passed from gasifier 3 to scrubbing zone 25. Because thetemperature of gasifier solids far exceeds dehydrogenation reactiontemperatures, this stream of hot solids from the gasifier is cooled byintroducing an effective amount of diluent into said stream of solidsvia line 41. Non-limiting diluents suitable for use herein includesteam, methane, nitrogen, hydrogen, hydrogen sulfide, carbon dioxide, agas, for example a fuel gas from line 40 or mixture thereof. Byeffective amount we mean that amount which will lower the temperature ofthe solids in line 35 to a range of about 450° C. to about 1100° C.,preferably from about 500° C. to 700° C. A stream of light paraffins isintroduced into line 35 via line 17. The stream contains a predominantamount of one or more C₂ to C₁₀ paraffins. By predominant amount we meanthat at least 50 wt. % of the stream will be composed of paraffins.Preferred are C₂ to C₁₀ alkanes and substituted alkanes; alkenes andsubstituted alkenes; alicyclic compounds, such as cyclohexane; alkylarylcompounds, wherein the alkyl group contains from about 2 to 10 carbonatoms, such as 1-butylbenzene;and naphtheno-aromatics, such astetrahydro-naphthalene. Preferred are C₂ to C₆ hydrocarbons, and morepreferred are C₂ to C₅ hydrocarbons, particularly the alkanes andalkenes. Typical hydrocarbon streams which can be used in the practiceof the present invention are petroleum refinery streams containing suchcomponents. Non-limiting examples of such stream include: the C₃ -C₄stream from reforming, coking, or hydrocracking; and the C₃ -C₅ streamfrom fluid catalytic cracking. The alkyl portions of the hydrocarbonsare dehydrogenated by contact with the hot coke particles in line 35.

It is within the scope of the present invention to improve conversionactivity by introducing an effective amount of one or more metalsselected from Groups I, such as Na and K; Group IIA, such as Mg and Ca;Group VA, such as V; Group VIA, such as Cr and Mo; Group VIIA, such asMn, and Group VIIIA, such as Fe, Co, and Ni. The groups referred to arefrom the Periodic Table of the Elements as published by Sargent-WelchScientific Co., Catalog Number S-18806, 1979. Preferred are K, Ca, V,Ni, and Fe. Effective amount, as used herein, means that amount whichwill cause an measureable increase in conversion activity, preferably atleast a 5% increase in activity, more preferably at least a 10% inactivity, over the case where no such metal are added. Compounds ormixtures of compounds containing said metals can be added with the feedto the fluid coker reactor, or may be introduced as a separate streaminto any of the vessels of the coking process unit.

Having thus described the present invention, and a preferred embodimentthereof, it is believed that the same will become even more apparent byreference to the following examples. It will be appreciated, however,that the examples, as well as the figure hereof, are presented forillustrated purposes and should not be construed as limiting theinvention.

Examples

Samples of gasifier coke from a commercial fluid coking process unitwere used for these examples. The surface area of coke was 168m² /g andwas comprised of 91.74 wt. % C; 0.03 wt. % H; 1.13 wt. % V; 0.48 wt. %Ni; and 0.91 wt. % Fe. The samples were placed in a fixed bed quartzreactor. Upon reaching the desired reaction temperature of about 650° C.under nitrogen, iso-butane feed was admitted to the catalyst bed at 1atm. Product samples were analyzed with a gas chromatograph and massspectrometer. A low surface area, about 1 m² /g, thermal reference(denstone) was included for comparison. The results are set forth in thetable below.

    ______________________________________                                                Comp.                                                                 Example Ex.      1        2      3      4                                     ______________________________________                                        Run     7-014    5-072    5-008  5-070  4-116                                 Number                                                                        Catalyst                                                                              Thermal  Gasifier Gasifier                                                                             Gasifier                                                                             Gasifier                                      Refer-   Coke     Coke   Coke   Coke                                          ence                                                                  Tempera-                                                                              575      575      605    625    650                                   ture (°C.)                                                             Residence                                                                             1        1        1      1      1                                     time (sec)                                                                    GHSV.sup.1                                                                            1066     1066     1066   1066   1066                                  Conversion                                                                            1.79     26.47    40.72  47.92  58.07                                 (wt. %)                                                                       Yield                                                                         (wt. %)                                                                       H.sub.2 0.03     0.70     0.84   1.43   1.29                                  CO.sub.2                                                                              0.04     0.26     0.35   0.42   0.36                                  CH.sub.4                                                                              0.16     0.65     1.93   3.05   4.42                                  C.sub.2 H.sub.6                                                                       0.00     0.03     0.10   0.15   0.24                                  C.sub.2 H.sub.4                                                                       0.00     0.04     0.12   0.23   0.37                                  C.sub.2 H.sub.8                                                                       0.01     0.37     0.88   1.17   1.28                                  C.sub.3 H.sub.6                                                                       0.43     0.95     2.72   4.38   5.67                                  n-C.sub.4 H.sub.10                                                                    0.13     0.23     0.22   0.17   0.08                                  1-Butene                                                                              0.00     0.03     0.05   0.06   0.08                                  Iso-    0.99     23.05    32.72  36.51  43.23                                 Butylene                                                                      t-2-Butene                                                                            0.00     0.03     0.05   0.06   0.07                                  c-2-Butene                                                                            0.00     0.03     0.08   0.05   0.06                                  >C.sub.4 's                                                                           0.00     0.10     0.66   0.24   0.92                                  Iso-C.sub.4 =                                                                         55.3     87.1     80.4   76.2   74.4                                  Select (%)                                                                    ______________________________________                                         .sup.1 GHSV = gas hourly space velocity = ml of gas per hour per ml of        catalyst per hour.                                                       

What is claimed is:
 1. An integrated process for converting a heavyhydrocarboneous chargestock to lower boiling products and for convertinglight paraffins to olefins, said process being performed in a fluidcoking process unit comprised of a fluid coking reactor, a heater, and agasifier, said fluid coking reactor containing a coking zone, ascrubbing zone located above the coking zone for collecting vapor phaseproducts, and a stripping zone for stripping hydrocarbons from solidparticles passing downwardly through the coking zone, which processcomprises:(a) introducing the heavy hydrocarbonaceous chargestock havinga Conradson carbon content of at least about 5 wt. %, into the cokingzone containing a fluidized bed of solid particles and maintained attemperatures from about 450° and 650° C. and pressure from about 0 to150 psig, wherein it is converted to lower boiling products whichincludes a vapor phase product, including normally liquid hydrocarbons,and wherein coke is deposited on the solid particles; (b) passing thevapor phase product to said scrubbing zone wherein entrained solidparticles are removed and wherein conversion products are removedoverhead; (c) passing a portion of the solid particles which remained inthe coking zone with coke deposited thereon downwardly through thecoking zone, past the stripping zone, thereby stripping hydrocarbonsfrom said solid particles and passing said solid particles to saidheating zone which contains a fluidized bed of solid particles andoperated at a temperature about 40° to 200° C. greater than that of thecoking zone; (d) recycling at least a portion of the heated solidparticles from the heating zone to said coking zone; (e) passing aportion of heated solid particles from the heater to the gasifier, saidgasifier being operated at a temperature from about 870° to 1100° C.thereby further heating said solid particles; (f) recycling a portion offurther heated solid particles from the gasifier to the heater; (g)passing another portion of further heated solid particles from thegasifier to the scrubbing zone; (h) introducing an effective amount of adiluent into the stream of solids passing from the gasifier to thescrubbing zone; (i) introducing a stream comprised of one or more C₄ toC₁₀ paraffins into the stream of hot (solids) solid particles passingfrom said gasifier to said scrubbing zone, at a point resulting inconversion of at least a portion of said paraffins to the correspondingolefins; and (j) passing the conversion product stream from thescrubbing zone to a fractionation zone wherein olefins are separatedfrom said stream.
 2. The process of claim 1 wherein the paraffin streamwhich is introduced into the solid particles passing from the heatingzone to the coking zone are C₄ to C₆ paraffins.
 3. The process of claim1 wherein the chargestock is selected from the group consisting of heavyand reduced petroleum crudes, petroleum atmospheric distillationbottoms, petroleum vacuum distillation bottoms, pitch, asphalt, bitumen,and liquid products derived from a coal liquefaction process.
 4. Theprocess of claim 3 wherein the chargestock has a Conradson carboncontent of about 5 to 40 wt. %.
 5. The process of claim 1 wherein thediluent is selected from the group consisting of steam, methane,nitrogen, carbon oxides, hydrogen sulfide, a fuel gas, and mixturesthereof.
 6. The process of claim further comprising the step of addingan effective amount of metal selected from Groups IA, IIA, VA, VIA,VIIA, and VIIIA of the Periodic Table of the Elements at any stage ofsaid integrated process.
 7. The process of claim 6 wherein the metal isselected from the group consisting of potassium, calcium, vanadium,nickel, and iron.